The present invention relates to an optical apparatus such as a so-called television lens or video lens. In particular, the present invention relates to an optical apparatus having an automatic focus (AF) function.
Moving-image pickup frequently incorporates a so-called full-time AF by which the position of a focus lens is controlled so as to always perform a focusing operation automatically (with a fixed cycle in a repeated manner).
However, the full-time AF may perform, depending on image-pickup conditions, the focusing operation for an object for which an operator does not intend to perform focusing. When an image of a subject for which the operator intends to perform focusing is picked up through a metal mesh for example, the focusing operation may be performed for the metal mesh or the background of the subject. Thus, an out of focus image may be picked up in the moving-image pickup because the focusing operation is performed for an unintended object for even a short time and thus defocusing from the subject for which the operator intends to perform focusing occurs.
In order to solve the problem described above, Japanese Patent Laid-Open No. 8-136799 has disclosed a technique in which an operator previously determines a permissible movable range within which a focus lens can be moved and the focus lens is moved only within this range to perform focusing.
However, in the technique disclosed in Japanese Patent Laid-Open No. 8-136799, when an in-focus position of the focus lens is detected for an object for which focusing is performed outside of the permissible movable range within which the focus lens can be moved, the focus lens is driven to an end of the permissible movable range. Specifically, an influence by the object for which the focusing operation should not be performed causes the drive of the focus lens which is otherwise not required.
Furthermore, this technique fixes the permissible movable range of the focus lens. Thus, in order to continuously maintain an in-focus state for a significantly moving subject, this technique requires a wide permissible movable range of the focus lens. In this case, when there is a plurality of objects that can be focused on at positions of the focus lens within the permissible movable range, the focusing operation may be performed for an object for which the operator does not intend to perform focusing.
For example, when an object that is not a focusing target passes before a subject as a focusing target, a hunting operation may be caused in which the focusing operation is performed for the object that is not the focusing target and the focusing operation is subsequently performed for the subject that is the focusing target.